The invention relates to a clock movement barrel shaft or a shaft for a clock movement barrel. It also relates to a clock movement barrel spring or a spring for a clock movement barrel. It further relates to a barrel including such a shaft and/or such a spring. It finally relates to a clock movement or a timepiece, notably a wristwatch, including such a shaft and/or such a spring.
The Professional Illustrated Dictionary Of Clockmaking (“Dictionnaire Professionnel Illustré de l'Horlogerie”) describes a classic construction of a barrel shaft for attaching a barrel spring. The shaft supports the drum and the cover of the barrel: bearing surfaces immobilize the drum and the cover in the axial direction and contact between the shaft, the drum and the cover allows pivoting of the drum about the shaft. The shaft further includes a cylindrical middle portion known as the core that is provided with a hook to which the barrel spring is attached by means of a rectangular opening (known in French as a “pigeonneau”) near the interior end of the spring.
The clock barrel must provide two apparently contradictory functions: on the one hand, supplying the energy necessary for driving the finishing wheels and for maintaining oscillation of the balance-hairspring by unwinding of the spring and, on the other hand, allowing winding of the same spring at any time. The cover and the drum must be able to pivot on the shaft to ensure correct functioning of the barrel.
Indeed, the barrel shaft is connected to a ratchet and rotation of the ratchet (driven by the winding system and/or the automatic system) enables winding of the spring, which is fastened to the shaft. The unwinding of the spring drives the drum and the cover as well as the finishing wheels that lead to the escapement and to the oscillator. The drum and the cover must therefore be able to pivot on the shaft, which must itself be able to pivot in a jewel bearing. This is not at all straightforward in practice, and is generally achieved by a staggered construction of the barrel shaft, with a succession of cylindrical surfaces with increasing diameters that define bearing surfaces, forming with the jewel bearings pivot surfaces for the pivoting of the shaft, with the drum and the cover, and finally a diameter for fastening the spring to the shaft.
A similar construction is known from the document CH295135. In a classic arrangement of this kind, the core diameter cannot be reduced for structural reasons. Indeed, the shaft must provide for pivoting and axial retention of the drum and the cover. Moreover, a ratchet is mounted on a square on the shaft, generally by means of a screw and a corresponding screwthread in the shaft. This classic construction makes it obligatory to stagger and therefore to increase the diameters of the barrel shaft, starting from the lower and upper ends of the shaft and as far as the core diameter.
Fixing the barrel spring by inserting the internal end of the spring in an opening provided in a spring fixing structure produced in the wall of a tube serving as the barrel shaft is known from the document GB1148042. The internal end of the barrel spring is deformed to cooperate with the fixing structure. A shaft has a square conformation adapted to cooperate with square bores provided in the barrel wheel and in the fixing structure. This solution leads to high mechanical deformation of the end of the barrel spring, which is not the optimum.
Fixing a barrel spring to a shaft by friction, with an opening of particular shape at the end of the spring to enable winding without increasing the thickness, is known from the document CH295135. The diameter of the attachment is then more or less equivalent to the diameter of the shaft, ignoring the additional thickness of one turn. This type of attachment with no mechanical connection is a priori relatively unreliable.
Attaching the spring by inserting the bent interior end of the spring into a longitudinal groove formed in the shaft is known from the document CH566044. This solution also leads to high mechanical deformation of the end of the spring, which is not the optimum.
Thus there is no known solution for fastening a barrel spring to a barrel shaft reliably, industrially, demountably and without severe plastic deformation of the spring and providing the possibility of minimizing the core diameter without having to modify the standard arrangement of the barrel, and in particular the pivoting of the drum and the cover on the shaft.
In another technical field very different from the clockmaking field, that of cameras, the document DE 859698 describes a camera barrel. The teachings of that document are not applicable to the problem of a clock barrel spring. In fact, with the barrel described in the above document it is not possible to maximize the space available for the spring and the construction used cannot be employed to produce a barrel with its cover and its drum, for the following reasons:                The document gives no indication concerning the placement of the drum and the cover, which must be able to pivot on the shaft. A traditional construction can therefore not be obtained based on the solution described in the document.        Additionally, this type of construction does not enable the user to wind the barrel while the camera is operating, which is a fundamental requirement for a clock barrel.        